Scabies is a parasitic skin infestation caused by the microscopic mite Sarcoptes scabiei var. hominis, which burrows into the outer layer of the skin to live and lay eggs. Since the mites continue to reproduce, the infestation cannot resolve on its own and requires active elimination. If scabies is not treated, consequences progress from worsening physical discomfort to serious, potentially life-threatening systemic health complications.
Escalation of Primary Symptoms
Untreated scabies allows the mite population to grow exponentially, which directly intensifies the physical symptoms experienced by the host. The female mite tunnels into the epidermis, where she deposits two to three eggs each day, which hatch into larvae within three to four days, continuing the cycle. This continuous proliferation leads to an increasing number of burrows and mites across the body over weeks or months.
The most prominent symptom, intense itching, is primarily an allergic reaction by the host’s immune system to the presence of mite proteins, feces, and eggs. This reaction typically appears four to six weeks after the initial infestation but can begin much faster upon re-exposure. As the mite population expands, the allergic response becomes more widespread and severe, often leading to a characteristic rash of small, red bumps or blisters. The rash, which initially appears in localized areas like the finger webs, wrists, and elbows, spreads to cover the trunk, limbs, and other regions, causing significant sleep disturbance and distress.
Risk of Secondary Bacterial Infection
Persistent scratching, driven by intense itching, damages the skin barrier. This creates small breaks and open sores, known as excoriations, that serve as entry points for bacteria. The resulting secondary bacterial infection is a common complication, particularly in tropical and resource-poor settings.
The most frequent bacterial pathogens involved are Staphylococcus aureus and Group A Streptococcus (GAS). These bacteria can cause impetigo, a superficial skin infection characterized by crusty sores. If left untreated, these infections can progress to more serious soft-tissue infections such as cellulitis, abscesses, or even sepsis, a life-threatening bloodstream infection. Furthermore, GAS-related skin infections are linked to secondary immune-mediated complications, including acute post-streptococcal glomerulonephritis, which can cause long-term kidney damage.
Development of Crusted Scabies
The most severe consequence of non-treatment is the development of crusted scabies, formerly known as Norwegian scabies. This form is defined by a massive, uncontrolled mite load, where a single person can host hundreds of thousands to millions of mites. Crusted scabies typically arises in individuals with compromised immune systems, such as the elderly, those with HIV/AIDS, patients undergoing chemotherapy, or people with conditions that impair the ability to scratch or sense the mites.
The physical manifestation includes thick, gray-white crusts and scaly plaques that form on the skin, often on the hands, feet, elbows, and knees. These crusts are packed with live mites and eggs, making the condition extremely contagious and easily transmissible through brief skin contact or contaminated objects like bedding. Due to immune suppression, the intense itching typical of classic scabies may be mild or absent, leading to delayed diagnosis and unchecked transmission.
Mandatory Treatment and Containment
Treatment for scabies is mandatory to alleviate symptoms and prevent the spread of the infestation, as it will not resolve spontaneously. Treatment requires prescription scabicidal medications, since over-the-counter products are ineffective against the mites. The standard medical approach involves topical agents, such as permethrin cream, which is applied to the entire body from the neck down and repeated after seven days to kill newly hatched mites.
For severe cases, including crusted scabies, combination therapy is often required, pairing topical permethrin with oral medications like ivermectin. Crucially, all close contacts, including household members and sexual partners, must be treated simultaneously, even if they show no symptoms, because an infested person can be contagious for weeks before symptoms appear. Environmental containment also involves laundering all clothing, bedding, and towels used in the last week in hot water to kill any mites and eggs that have fallen off the host.